Due to a lack of a long-range order of an atomic arrangement of an amorphous alloy, neither dislocation nor grain boundary exists in the structure of the alloy. Therefore, compared with ordinary polycrystalline metal materials, amorphous alloys have merits such as high intensity, corrosion resistance, and abrasion resistance, and may be used as raw materials for manufacturing microelectronic devices, sports utilities, luxury goods, consumer electronics, and the like. A general method for manufacturing an amorphous alloy is to cool an alloy melt quickly to be below a glass transformation temperature (Tg) at a certain cooling speed. The extremely fast cooling speed avoids crystal nucleation and growth, and finally accomplishes a completely amorphous structure. If the cooling speed required for turning a material into an amorphous structure is lower, it is easier to form a large-sized amorphous structure of the material. In alloy systems such as Zr-based, palladium-based, magnesium-based, iron-based, copper-based, and lanthanum-based alloy systems, the critical cooling speed of specific alloys is less than 10 K/second in magnitude, and bulk amorphous alloys of a thickness of a centimeter magnitude may be manufactured through copper mold casting.
Generally, a critical diameter that can form a cast round bar of a completely amorphous structure is used as glass forming ability (GFA) of the alloy. The glass forming ability of the alloy primarily depends on chemical components of the alloy. Complexity and diversity of the alloy components can reduce the critical cooling speed of forming the amorphous structure and improve the glass forming ability of the alloy. Among them, a multi-element Zr-based amorphous alloy is an amorphous alloy that has ever been discovered so far having a good glass forming ability and superb mechanical and machining properties, and taking on the best application prospect of structural materials.
The Zr-based amorphous alloys that have been developed so far for forming an amorphous structure in the world centrally exist in the Zr-TM-Al or Zr-TM-Be (TM is Ti, Cu, Ni, or Co) system. With certain components of such alloys, a melt may cool down to form an amorphous round bar material of a diameter greater than 10 mm. Currently, the manufacturing of such alloys occurs primarily in labs. The oxygen content in an alloy is generally less than 200 ppm. Therefore, the oxygen content existent in the raw material and introduced in the manufacturing process must be controlled strictly.
For example, the following alloy formula can form an amorphous structure of a certain size after being cast:(Zr,Hf)aMbAlc,
where M is Ni, Cu, Fe, Co, or any combination thereof; a, b, and c are atomic percents, 25≦a≦85, 5≦b≦70, and 0<c≦35. Preferably, after vacuum melting and ordinary copper mold casting, the Zr50Cu40Al10 alloy can form a completely amorphous round bar of a 10 mm diameter, that is, have a glass forming ability of 10 mm.
To further enhance the glass forming ability of the alloy, a proper amount of Ni is generally added into the alloy, and combines with Cu into a specific formula. For example, after 5 at. % of Ni is added into the alloy, a four-element Zr55Cu30Ni5Al10 alloy is obtained, whose glass forming ability is up to 30 mm. A general manufacturing method is as follows: Place a specific quantity of raw materials of a specific formula into a vacuum smelting furnace, adjust the vacuum degree to 5×10−3 Pa, and then charge with 0.05 MPa argon as protection gas; after homogeneous smelting and cooling with the furnace, obtain a master alloy; subsequently, place the master alloy into an induction furnace for re-melting, and then spray and cast the master alloy into a copper mold to obtain amorphous alloy bars.
The GFA of a Zr-based alloy in the prior art is very sensitive to oxygen content of the alloy. Because cohesion of zirconium and oxygen occurs very easily, zirconium oxide or zirconium/oxygen clusters can be generated easily in the alloy melt. They may serve as a core of non-homogeneous nucleation, and reduce the GFA of the alloy. Under ordinary laboratory or industrial conditions, a certain amount of oxygen is inevitably introduced into the Zr-based amorphous alloy. Therefore, expensive high-purity raw materials have to be used in the production process, and a high vacuum degree is required in smelting and casting processes. The required vacuum degree is over 10−2 Pa or even 10−3 Pa to prevent decrease of the amorphous GFA caused by high oxygen content in the alloy. High-purity (a purity of over 99.9%) raw materials and stringent protection atmosphere lead to very high costs of manufacturing a Zr-based amorphous alloy, and make mass production impracticable. Ordinary industrial raw materials in the market are not good enough for manufacturing components and products of an amorphous structure of specific dimensions.